Semiconductor optical device having current-confined structure

ABSTRACT

Provided is a semiconductor optical device having a current-confined structure. The device includes a first semiconductor layer of a first conductivity type which is formed on a semiconductor substrate and includes one or more material layers, a second semiconductor layer which is formed on the first semiconductor layer and includes one or more material layers, and a third semiconductor layer of a second conductivity type which is formed on the second semiconductor layer and includes one or more material layers. One or more layers among the first semiconductor layer, the second semiconductor, and the third semiconductor layer have a mesa structure. A lateral portion of at least one of the material layers constituting the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer is recessed, and the recess is partially or wholly filled with an oxide layer, a nitride layer or a combination of them. The semiconductor optical device having the current-confined region is mechanically reliable, highly thermally conductive, and commercially preferable and can be used in a wavelength range for optical communications.

The present patent application is a Continuation of application Ser. No.10/699,127, filed Oct. 30, 2003 and assigned U.S. Pat. No. 7,230,276,which claims the priority of Korean Patent Application No. 2002-69586,filed on Nov. 11, 2002, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor optical devices, and moreparticularly, to a semiconductor optical device having acurrent-confined structure.

2. Description of the Related Art

Typically, semiconductor optical devices are applicable in variousfields owing to their long lifetime and high optical conversionefficiency. In particular, the semiconductor optical devices haveattracted considerable attention as active devices such as lightsources, for communications with a wavelength range of 1.2 to 1.7 μm,and detectors. In such a semiconductor optical device, a gain region isformed between semiconductor layers of opposite types, i.e., a p-typesemiconductor layer and an n-type semiconductor layer, which aretypically grown over InP or GaAs substrates, and a current-confinedstructure is formed in at least one of the semiconductor layers. Then,electrodes are formed on the upper and lower semiconductor layers so asto operate the optical device. The current-confined structure performs avery important function for the operation of the optical device.

The current-confined structure of the semiconductor optical device canbe formed by various conventional methods. For example, a method oflaterally oxidizing an Al(Ga)As semiconductor layer using wetoxidization, a method of laterally oxidizing an InAlAs layer or anAlAsSb layer using wet oxidization, a method of forming an undercutcurrent-confined region by etching a semiconductor layer, a method ofperforming an ion implantation process and an annealing process, and amethod of etching an adjacent portion of a tunnel junction andperforming a re-growth process have been employed.

However, the foregoing methods of forming a current-confined structureof a semiconductor optical device have the following problems.

Firstly, a semiconductor optical device having a current-confinedstructure that is formed by laterally oxidizing an AlAs layer using wetoxidization has excellent characteristics. However, in this method, again medium grown over a GaAs substrate cannot reliably provide awavelength range of longer than 1 μm. Therefore, a new method of forminga current-confined structure applicable in a long-wavelength range ofapproximately 1.55 μm is required.

Secondly, a current-confined structure, obtained by laterally oxidizingan InAlAs layer or an AlAsSb layer using wet oxidization, iscommercially adverse because the wet oxidization should be performed ata high temperature of 500° C. for quite a long time and a crystal growthincluding Sb is required. Thirdly, the method of forming an undercutcurrent-confined region by selectively etching a semiconductor layermakes the semiconductor optical device mechanically unreliable.

Fourthly, when a current-confined structure is formed using an ionimplantation process and an annealing process, it is difficult to curecrystalline structures formed in an unwanted region. Finally, the methodof etching an adjacent portion of a tunnel junction and performing are-growth process is very complicated and tends to get good results onlyfrom optical devices grown using commercially adverse molecular beamepitaxy.

SUMMARY OF THE INVENTION

The present invention provides a semiconductor optical device having acurrent-confined structure which can be used in a wavelength range foroptical communications and is mechanically reliable, highly thermallyconductive, and commercially preferable.

In accordance with an aspect of the present invention, there is provideda semiconductor optical device comprising a first semiconductor layer ofa first conductivity type which is formed on a semiconductor substrateand includes one or more material layers, a second semiconductor layerwhich is formed on the first semiconductor layer and includes one ormore material layers, and a third semiconductor layer of a secondconductivity type which is formed on the second semiconductor layer andincludes one or more material layers. Here, the first conductivity typeis opposite to the second conductivity type. One or more layers amongthe first semiconductor layer, the second semiconductor layer, and thethird semiconductor layer have a mesa structure. A lateral portion of atleast one of the material layers constituting the first semiconductorlayer, the second semiconductor layer, and the third semiconductor layeris recessed, and the recess is partially or wholly filled with an oxidelayer, a nitride layer or a combination of them.

Preferably, when the first semiconductor layer is a p-type semiconductorlayer, the third semiconductor layer is an n-type semiconductor layerand when the first semiconductor layer is an n-type semiconductor layer,the third semiconductor layer is a p-type semiconductor layer. Thesecond semiconductor layer may be a p-type semiconductor layer, ann-type semiconductor layer, or an undoped semiconductor layer.

While the optical device is operated, the first semiconductor layer andthe third semiconductor layer serve as confinement-conducting regions,and the second semiconductor layer serves as a gain region. The oxidelayer, the nitride layer or a combination of them may be formed of ZnO,MgO, TiO₂, Ta₂O₅, ZrO₂, HfO₂, SiO₂, Al₂O₃, Si₃N₄, AlN, AlON or acombination of them.

For a surface emitting optical device, at least one reflecting mirrormay be further formed on the both sides of overall layers so as to beparallel with the semiconductor layers, thereby making output lightperpendicular to the semiconductor layer through the reflecting mirror.For a edge-emitting optical device, at least one reflecting mirror maybe further formed so as to be perpendicular to the first semiconductorlayer through the third semiconductor layer, thus making output lightparallel with the first semiconductor layer through the thirdsemiconductor layer.

In accordance with another aspect of the present invention, there isprovided a semiconductor optical device comprisingconfinement-conducting regions having semiconductor layers, each ofwhich includes one or more material layers, and a gain region having asemiconductor layer, which is formed between the confinement-conductingregions and includes one or more material layers. Theconfinement-conducting region(s) and the gain region have a mesastructure. A lateral portion of at least one of the material layersconstituting the semiconductor layers of the confinement-conductingregions and the gain region is recessed, and the recess is partially orwholly filled with an oxide layer, a nitride layer or a combination ofthem.

The oxide layer, the nitride layer or a combination of them may beformed using atomic layer deposition (ALD). The oxide layer, the nitridelayer or a combination of them. The oxide layer, the nitride layer or acombination of them may be formed of ZnO, MgO, TiO₂, Ta₂O₅, ZrO₂, HfO₂,SiO₂, Al₂O₃, Si₃N₄, AlN, AlON or a combination of them.

The semiconductor layers constituting the confinement-conducting regionsmay be a p-type semiconductor layer, an n-type semiconductor layer, or acombination of them. The semiconductor layer constituting the gainregion may be a p-type semiconductor layer, an n-type semiconductorlayer, or an undoped semiconductor layer.

A layer including tunnel junction for hole carrier supplying may befurther formed in one of the confinement-conducting regions. In thiscase, the confinement-conducting region has a composite conductivitytype and consists of n-type and p-type semiconductor layers.

At least one reflecting mirror may be further formed so as to beparallel with the confinement-conducting regions and the gain region,thus making output light perpendicular to the confinement-conductingregions and the gain region. At least one reflecting mirror may befurther formed so as to be perpendicular to the confinement-conductingregions and the gain region, thus making output light parallel with theconfinement-conducting regions and the gain region.

As described above, the semiconductor optical device of the presentinvention has the current-confined structure which can be used in awavelength range for optical communications and is mechanicallyreliable, highly thermally conductive, and commercially preferable.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings in which:

FIGS. 1 through 3 are cross-sectional views of a semiconductor opticaldevice having a current-confined structure according to an embodiment ofthe present invention, for illustrating a method for fabricating thesame;

FIG. 4 are cross-sectional view of a semiconductor optical device havinga current-confined structure according to another embodiment of thepresent invention;

FIG. 5 is a conduction band diagram of a semiconductor optical deviceaccording to the present invention;

FIG. 6 is a graph showing current-voltage characteristics of thesemiconductor optical device having the current-confined structureaccording to the present invention; and

FIGS. 7 and 8 show cases where the semiconductor optical device havingthe current-confined structure is used in a edge-emitting optical deviceand a surface (bottom)-emitting optical device, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which preferred embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure is thorough and complete and fully conveys theconcept of the invention to those skilled in the art. In the drawings,the shape of elements is exaggerated for clarity. Further, it will beunderstood that when a layer is referred to as being “on” another layeror substrate, it can be directly on the other layer or substrate, orintervening layers may also be present.

FIGS. 1 through 3 are cross-sectional views of a semiconductor opticaldevice having a current-confined structure according to an embodiment ofthe present invention, for illustrating a method for fabricating thesame.

Referring to FIG. 1, a first semiconductor layer 12 of a firstconductivity type, for example, a p-type semiconductor layer or ann-type semiconductor layer, is formed on a semiconductor substrate 10.The semiconductor substrate 10 may be an InP substrate. While the firstsemiconductor layer 12 may be formed of one or more Group III-Vsemiconductor materials, in this embodiment, the first semiconductorlayer 12 of FIG. 1 is formed of two material layers 12 a and 12 b forconvenience. The first semiconductor layer 12 can serve as aconfinement-conducting region during operations of the semiconductoroptical device.

A second semiconductor layer 14 having a recess 15 is formed on thefirst semiconductor layer. While the second semiconductor layer 14 maybe formed of one or more Group III-V semiconductor materials, in thisembodiment, the second semiconductor layer 14 of FIG. 1 is formed of onematerial layer for convenience. The second semiconductor layer 14 may beformed of a p-type semiconductor layer, an n-type semiconductor layer,an undoped semiconductor layer, or a combination thereof. The secondsemiconductor layer 14 can serve as a gain region during operations ofthe semiconductor optical device.

A third semiconductor layer 16 of a second conductivity type, forexample, an n-type semiconductor layer or a p-type semiconductor layer,is formed on the second semiconductor layer 14. Here, the secondconductivity type is opposite to the first conductivity type. That is,when the first semiconductor layer 12 is a p-type semiconductor layer,the third semiconductor layer 16 is formed of n-type semiconductormaterial(s), and when the first semiconductor layer 12 is an n-typesemiconductor layer, the third semiconductor layer 16 is formed ofp-type semiconductor material(s). While the third semiconductor layer 16may be formed of one or more Group III-V semiconductor materials, inthis embodiment, the third semiconductor layer 16 of FIG. 1 is formed offour material layers 16 a, 16 b, 16 c, and 16 d for convenience. Thethird semiconductor layer 16 can serve as a confinement-conductingregion during operations of the semiconductor optical device.

The material layers constituting the first semiconductor layer 12, thesecond semiconductor layer 14, and the third semiconductor layer 16 areformed of materials capable of growing over the InP substrate 10, suchas InP, InGaAs, InAlGaAs, InAlAs, and InGaAsP, using metal-organic vaporphase epitaxy.

One or more layers of the first semiconductor layer 12, the secondsemiconductor layer 14, and the third semiconductor layer 16 have a mesastructure. Further, after forming the mesa structure, a lateral portionof the second semiconductor layer 14 is selectively etched by a wet etchprocess using a solvent of the phosphorus acid group or the hydrochloricacid group, thereby forming the recess 15. The recess 15 may be formedusing other etching processes having a high etch selectivity withrespect to the Group II-V semiconductor materials constituting the firstsemiconductor layer 12 and the third semiconductor layer 16. An undercutetching-profile can be controlled by adjusting the composition of theGroup III-V semiconductor materials constituting the first semiconductorlayer 12, the second semiconductor layer 14, and the third semiconductorlayer 16. Unlike FIG. 1, the recess 15 may be formed in at least one ofthe material layers constituting the first semiconductor layer 12 or thethird semiconductor layer 16 in place of the second semiconductor layer14.

Referring to FIG. 2, to fill the recess 15, a highly thermallyconductive oxide layer, nitride layer or a combination of them 18, isformed on the semiconductor substrate 10 and on the sidewalls of thefirst semiconductor layer 12, the second semiconductor layer 14 and thethird semiconductor layer 16. As shown in FIG. 2, the recess 15 may bepartially or wholly filled with the oxide layer, nitride layer or acombination of them 18, Etching faces exposed through the recess 15 maycause leakage current and non-radiative recombination, and this resultsin degradation of the semiconductor optical device. In the presentinvention, the oxide layer or the nitride layer] 18 is deposited on theetching faces exposed through the recess 15. Thus, degradation of thesemiconductor optical device can be reduced and also, the filled theoxide layer, nitride layer or a combination of them 18 makes thesemiconductor optical device mechanically reliable.

The oxide layer, nitride layer or a combination of them 18 is formed ofZnO, MgO, TiO₂, Ta₂O₅, ZrO₂, HfO₂, SiO₂, Al₂O₃, Si₃N₄, AlN, AlON or acombination of them. When the oxide layer, nitride layer or acombination of them 18 is formed of the aluminum oxide layer, which ishighly thermally conductive as compared with the semiconductor layers,such as InAlGaAs, InGaAsP, InAlAs, and InGaAs, formed on thesemiconductor substrate 10, the semiconductor optical device hasexcellent heat dissipation.

In particular, a light source device for optical communications , grownover a semiconductor substrate 10 like the InP, is prone to degradationdue to a large gain drop with an increase in the temperature. However,the semiconductor optical device of the present invention has excellentheat dissipation, thus solving this problem. Further, if thesemiconductor optical device of the present invention is used in a laserdevice, because the recess 15 is filled with the oxide layer, nitridelayer or a combination of them 18, a difference in the refractive indexbetween a light-emitting core region and an adjacent cladding region canbe reduced. As a result, a transverse mode characteristic of laser lightcan be improved.

Filling the recess 15 with the oxide layer, nitride layer or acombination of them 18 employs an ALD process. In particular, when thealuminum oxide layer is formed of trimethyl aluminum (TMA) and H₂O usingALD, a dense thin layer having a refractive index of about 1.67 can bedeposited at a relatively low temperature of 200˜400° C. The ALD processis commercially available.

Referring to FIG. 3, a first electrode 20 and a second electrode 22 areformed on the top of the third semiconductor layer 16 and on the bottomof the semiconductor substrate 10, respectively. The second electrode 22may be formed on the first semiconductor layer 12 in place of the bottomof the overall semiconductor layers or substrate 10. As shown in FIG. 3,when a voltage is applied to the first and second electrodes 20 and 22,the arrows in the drawing indicate a current flow. The current appliedto the third semiconductor layer 16 converges into the secondsemiconductor layer 14 and then spreads again through the firstsemiconductor layer 12.

FIG. 4 are cross-sectional view of a semiconductor optical device havinga current-confined structure according to another embodiment of thepresent invention. In FIG. 4, the same reference numerals as in FIGS. 1through 3 represent the same members.

Referring to FIG. 4, the recess 19 is formed in the layer(s) ofconfinement-conducting regions 17 a and 17 b. The confinement-conductingregions 17 a and 17 b are formed of five and three material layers forconvenience, respectively. The gain region 15 is formed between theconfinement-conducting regions 17 a and 17 b and neighbors oppositeconductivity type semiconductor layers on each side. A layer includingtunnel junction for hole carrier supplying may be further formed in oneof the confinement-conducting regions 17 a and 17 b. In this case, aconfinement-conducting regions 17 a and 17 b consists of n-type andp-type semiconductor layers.

FIG. 5 is conduction band diagram of the semiconductor optical deviceaccording to the present invention. In FIG. 5, the same referencenumerals as in FIGS. 1 through 4 represent the same members.

As shown in FIG. 5, the confinement-conducting region 21 includes acarrier confinement layers and the conducting layers for carrierinjection. The injected carriers 27 from electrode 20 and 22 areconfined around the gain region 25 between the confinement-conductingregions 21.

As described above, the semiconductor optical device of the presentinvention has the mesa structure with the recess by forming acurrent-flowing region, for example, the second semiconductor layer 14,using lateral selective etching. Also, in the present invention, becausethe recess is filled with a material having excellent insulationcharacteristic and thermal conductivity, the semiconductor opticaldevice has a current-confined structure which is mechanically reliableand has excellent heat dissipation. As a result, when a voltage isapplied to the electrodes of the semiconductor optical device, currentcan effectively flow through the second semiconductor layer. Although,in the present embodiment, the first semiconductor layer 12 and thethird semiconductor layer 16 serve as confinement-conducting regions andthe second semiconductor layer 14 serves as a gain region, as long asthe gain region is formed between the confinement-conducting regions,the confinement-conducting regions and the gain region may be changedaccording to where the recess is formed.

FIG. 6 is a graph showing current-voltage characteristics of thesemiconductor optical device having the current-confined structureaccording to the present invention.

Specifically, as shown in FIG. 6, the semiconductor optical devicefilled with the oxide layer (Al₂O₃) (illustrated as a solid line anddenoted by reference letter a) has lower leakage current than thesemiconductor optical device not filled with the oxide layer (Al₂O₃)(illustrated as a dotted line and denoted by reference letter b).

FIGS. 7 and 8 show cases where the semiconductor optical device havingthe current-confined structure is used in a edge-emitting optical deviceand a surface (bottom)-emitting optical device, respectively. In FIGS. 7and 8, the same reference numerals as in FIGS. 1 through 3 represent thesame members.

Specifically, FIG. 7 shows the edge-emitting optical device. In FIG. 7,a reflecting mirror 24 is formed so as to be perpendicular to thesemiconductor layer 23, i.e., the first semiconductor layer through thethird semiconductor layer 12, 14, and 16 of FIGS. 1 through 3, therebymaking output light 26 parallel with the first semiconductor layerthrough the third semiconductor layer 12, 14, and 16. FIG. 8 shows thesurface-emitting optical device. In FIG. 8, a reflecting mirror 24 isformed so as to be parallel with the first semiconductor layer throughthe third semiconductor layer 12, 14, and 16 of FIGS. 1 through 3,thereby making output light 28 perpendicular to the first through thirdsemiconductor layers 12, 14, and 16.

Further, the semiconductor optical device having the current-confinedstructure according to the present invention can be used inedge-emitting semiconductor lasers, edge light-emitting diodes,surface-emitting semiconductor lasers, surface light-emitting diodes,light-receiving diodes, semiconductor optical amplifiers, and opticaldetectors.

As described above, in the semiconductor optical device according to thepresent invention, a semiconductor layer is selectively etched so as toform a recess, which is filled with a highly thermally conductive oxidelayer, nitride layer or a combination of them. Thus, the semiconductoroptical device has a current-confined structure.

As a result, the semiconductor optical device according to the presentinvention is mechanically reliable and highly thermally conductive.Also, because the recess is filled with the oxide layer, the nitridelayer or a combination of them using ALD so as to reduce leakage currentat the etching faces, the semiconductor optical device is mechanicallyreliable and commercially preferable.

Consequently, the semiconductor device according to the presentinvention has a current-confined structure suitable for a wavelengthrange of optical communications which is mechanically reliable, highlythermally conductive, and commercially preferable. Further, thesemiconductor optical device of the present invention is applicable invarious technical fields of, for example, light sources and detectingdevices, optical communications, light-emitting diodes and lasers, andvertical cavity surface-emitting lasers.

While the present invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A semiconductor optical device comprising: confinement-conductingregions having semiconductor layers, each of the confinement-conductingregions including one or more material layers; and a gain region havinga semiconductor layer, which is formed between theconfinement-conducting regions and includes one or more material layers,wherein the confinement-conducting regions and the gain region have amesa structure, and a lateral portion of at least one of the materiallayers constituting the semiconductor layers of theconfinement-conducting regions and the gain region is recessed, and therecess is formed by selectively etching the lateral portion of at leastone of the material layers and the material layers surrounding therecess have different etching rates compared to at least one of thematerial layers constituting the semiconductor layer of the gain region,and the recess is partially or wholly filled by deposition with an oxidelayer, a nitride layer or a combination of them, wherein at least onereflecting mirror is further formed so as to be parallel with theconfinement-conducting regions and the gain region such that outputlight is perpendicular to the confinement-conducting regions and thegain region.
 2. The device of claim 1, wherein the oxide layer or thenitride layer or a combination of them is formed using atomic layerdeposition.
 3. The device of claim 1, wherein the oxide layer or thenitride layer or a combination of them is formed of one of a ZnO, MgO,TiO₂, Ta₂O₅, ZrO₂, HfO₂, SiO₂, Al₂O₃, Si₃N₄, AlN, AlON and a combinationof them.
 4. The device of claim 1, wherein the semiconductor layerconstituting the confinement-conducting regions is one of a p-typesemiconductor layer, an n-type semiconductor layer and a combination ofthem.
 5. The device of claim 1, wherein the semiconductor layerconstituting the gain region is one of a p-type semiconductor layer, ann-type semiconductor layer, and an undoped semiconductor layer.
 6. Asemiconductor optical device comprising: confinement-conducting regionshaving semiconductor layers, each of which includes one or more materiallayers; and a gain region having a semiconductor layer, which is formedbetween the confinement-conducting regions and includes one or morematerial layers, wherein the confinement-conducting regions and the gainregion have a mesa structure, and a lateral portion of at least one ofthe material layers constituting the semiconductor layers of theconfinement-conducting regions and the gain region is recessed, and therecess is formed by selectively etching the lateral portion of at leastone of the material layers and the material layers surrounding therecess have different etching rates compared to at least one of thematerial layers constituting the semiconductor layer of the gain region,and the recess is partially or wholly filled by deposition with an oxidelayer, a nitride layer or a combination of them.
 7. The device of claim6, wherein the oxide layer, the nitride layer or a combination of themis formed using atomic layer deposition.
 8. The device of claim 6,wherein the oxide layer or the nitride layer or a combination of them isformed of one of a ZnO, MgO, TiO₂, Ta₂O₅, ZrO₂, HfO₂, SiO₂, Al₂O₃,Si₃N₄, AlN, AlON and a combination of them.
 9. The device of claim 6,wherein the semiconductor layer constituting the confinement-conductingregions is one of the group consisting of a p-type semiconductor layer,an n-type semiconductor layer and a combination of them.
 10. The deviceof claim 6, wherein the semiconductor layer constituting the gain regionis one of a p-type semiconductor layer, an n-type semiconductor layer,and an undoped semiconductor layer.
 11. A semiconductor optical devicecomprising: confinement-conducting regions having semiconductor layers,each of which includes one or more material layers; and a gain regionhaving a semiconductor layer, which is formed between theconfinement-conducting regions and includes one or more material layers,wherein the confinement-conducting regions and the gain region have amesa structure, and a lateral portion of at least one of the materiallayers constituting the semiconductor layers of theconfinement-conducting regions and the gain region is recessed, and therecess is formed by selectively etching the lateral portion of at leastone of the material layers and the material layers surrounding therecess are not selectively etched and the recess is partially or whollyfilled by deposition with an oxide layer, a nitride layer or acombination of them and wherein at least one reflecting mirror isfurther formed so as to be perpendicular to the confinement-conductingregions and the gain region such that output light is parallel with theconfinement-conducting regions and the gain region.